NIRI SV observation 3

	Status: in preparation Data link: not yet available Assessment: not yet available

Mode:	Wide-field imaging
Additional instrument verification:	Tests both narrow-band imaging (low-background) and thermal (high-background) imaging modes with the f/6 camera. Tests data reduction pipeline for imaging data and array performance in very low background.
Telescope verification:	Uses both calunit and sky flats.
Proposed observing sequence:	not yet available
OT program file:	not yet available
Science background:	Imaging the Detailed Structure of PDRs The existence of high-density 'clumps' in nearby photodissociation regions (M17, galactic center disk) has frequently been inferred to explain observations of these regions. A consensus has been reached that PDRs can no longer be considered as homogeneous slabs of material. However, the questions of whether the clumps control the structure of the PDR and how this influences the models are still debated. Mapping of two well-studied regions in the 1-0 S(1), 2-1 S(1), Br gamma, and 3.28um filters is proposed. The ratio of 1-0 S(1)/2-1 S(1) is sensitive to density, providing a clear picture of changes in density which is not afforded by intensity maps. An intensity map may show enhanced emission due to geometrical or surface density effects alone. A study of Orion by Ramsay Howat et al. (1999) demonstrated the success of this technique.
Target(s):
	Object	approx. RA (2000)	approx. dec (2000)
	M17	18 h 18 m	-16 deg
	GC disk	17 h 43 m	-29 deg
Observing condition constraints:	image quality: 50%-ile sky transparency (clouds): 50%-ile sky transparency (water vapour): 80%-ile sky background: 80%-ile max air mass: 2.0
Observing time requirements:	8 hours total for M17; 4 hours for the GC disk
SV team member(s) responsible for assessment:	Suzanne Ramsay Howat

Last update October 29, 1999; Joe Jensen